Bottles made of plastic such as PET bottles are easily produced by molding and suitable for mass production, and they have excellent properties such as high mechanical strength and a light weight, so that they are used as containers for filling various liquids therein in wide fields.
In particular, large quantities of them are used as beverage containers for various beverages, mineral water, and the like, in recent years.
With regard to the volume of the bottle, many kinds of bottles are available as will suit market demands. For example, containers having a volume of about 2,000 ml are used as large-volume containers. Concerning the form of the containers, there are conventionally employed containers having a transverse-sectional form of a circle or containers having a transverse-sectional form of a rectangle or square formed by taking account of storability thereof in a refrigerator.
In a large-volume bottle, a waist portion having a form constricted mainly along the circumferential direction is formed nearly in the center in the height direction of the body portion for imparting the body portion with necessary strength. The waist portion not only works as a reinforcing portion but also works as a grasping portion which is caught with fingers when the bottle is held with one hand, so that it improves the bottle in easiness of handling.
Meanwhile, in recent years, the wall thickness of bottles is decreasing with the tendency to decrease the weight of bottles together with natural resources saving, so that the strength of bottles is declining as a whole. In thin-wall bottles of which the weight is decreased, it is required to form side beads, etc., on the body portion to impart the bottle with necessary strength and restoring strength so that the denting and distortion of the bottle are prevented (for example, see Patent Document 1).
Patent Document 1 JP-A-2004-250063